Study of metadynamic recrystallization behaviors in a low alloy steel

The metadynamic recrystallization behaviors in deformed 42CrMo steel were investigated by isothermal interrupted hot compression tests on Gleeble-1500 thermo-mechanical simulator. Compression tests were performed using double hit schedules at temperatures of (850–1150) °C, strain rates of (0.01–1) s^?1 and inter-stage delay time of (1–50) s. The kinetic equations have been proposed to predict the metadynamic recrystallization behaviors in hot compressed 42CrMo steel. Comparisons between the experimental and predicted results were carried out. Results show that the effects of deformation parameters, including strain rate and deformation temperature, on the softening behaviors in the two-pass hot deformed 42CrMo steel are significant. However, the deformation degree (beyond the peak strain) has little influence on the metadynamic recrystallization behaviors in 42CrMo steel. The predicted results well agree with the experimental ones, which indicate that the proposed kinetic equations can give a precise estimate of the softening behaviors and microstructural evolution for the hot deformed 42CrMo steel.     

42CrMo钢亚动态再结晶行为研究

利用双道次热压缩的方法,研究了42CrMo钢在高温变形道次间隔时间内奥氏体的亚动态再结晶行为。基于试验结果,建立了42CrMo钢的亚动态再结晶动力学模型。讨论了工艺参数对亚动态再结晶晶粒大小的影响规律。结果表明,42CrMo钢很容易发生亚动态再结晶,道次间隔时间越长,材料软化程度增大,亚动态再结晶越明显。随着变形温度的升高、应变速率的增大,完全亚动态再结晶所需时间迅速减少;将亚动态再结晶动力学模型的预测结果与试验结果进行比较,二者吻合较好;变形温度越低、应变速率越大,亚动态再结晶晶粒越小。相同形变条件下,亚动态再结晶晶粒明显细于静态再结晶晶粒。     

35CrMo钢热变形机制的模拟研究

以弯曲镦锻 3 5 Cr Mo钢火车曲轴为例 ,通过将该钢以 90 0℃～ 1 2 5 0℃变形温度 ;0 .0 5 s-1、0 .5s-1、1 .0 s-1的应变速率 ;在 Greeble-1 5 0 0试验机上进行压缩 1 5 %～ 80 %的热变形实验 ,和随后进行的微观组织分析得出了 :材料热变形屈服应力变化模型 ;材料热变形本构关系 ;动态与静态再结晶模型和热加工参数与微观组织变化的相关性资料。描绘了在 1 2 5 0℃ ,应变速率为 1 .0 s-1时 ,3 5 Cr Mo钢热变形应力应变曲线和相应的再结晶组织。通过对 3 5 Cr Mo钢在高温大变形条件下 ,试件内部各区域晶粒尺寸的回归计算 ,验证了该钢热变形晶粒计算模型。所得出的实验结果和计算模型为热成形工艺分析和质量控制提供了科学的依据     

Numerical simulation and experimental verification of microstructure evolution in a three-dimensional hot upsetting process

The hot compression tests of 42CrMo steel were performed in the temperature range of 850–1150 °C at strain rates of 0.01–10 s^?1 and deformation degrees of 10–60% on Gleeble-1500 thermo-simulation machine. The optical microstructures in the center region of the section plane were examined. Based on the results from thermo-simulation experiments and metallographic analysis, the dynamic recrystallization mathematical models of 42CrMo steel were derived. The effects of processing parameters, including the strain rate and deformation temperature, on the microstructure evolution of 42CrMo steel hot upsetting process were discussed by integrating the thermo-mechanical coupled finite element method with the derived microstructure evolution models. The fraction of dynamic recrystallization and dynamic recrystallization grain sizes during the hot upsetting process of 42CrMo steel were predicted. The results show that the effects of strain rates and deformation temperatures on the microstructure evolution of 42CrMo steel hot upsetting process are significant, and a good agreement between the predicted and experimental results was obtained, which confirmed that the derived dynamic recrystallization mathematical models can be successfully incorporated into the finite element model to predict the microstructure evolution of hot upsetting process for 42CrMo steel.     

热变形对42CrMo钢奥氏体晶粒尺寸影响的试验研究

采用热压缩试验与有限元模拟相结合的方法,研究42CrMo钢热加工过程中临界变形、多道次压下、道次间隔时间和完全再结晶后的保温时间对奥氏体晶粒长大的影响规律。结果显示,在热变形过程中,增大道次压下量,缩短道次间隔时间,有利于晶粒细化。在热变形的最后工序中,应尽量避免容易引起晶粒粗大的临界变形;热变形完成后,应尽量缩短保温时间,防止再结晶后的晶粒异常长大;在1050℃温度附近,42CrMo钢的保温时间不应超过30min。     

ZK60镁合金热变形过程中的应变强化与动态再结晶行为(英文)

研究ZK60合金的高温流变应力行为。分别采用Kocks-Mecking模型和Avrami方程对合金的应变强化和动态再结晶过程进行模拟,在此基础上,构建一个考虑合金动态再结晶软化的流变应力方程并对流变应力进行预测。结果表明:预测曲线与实验结果具有很高的相关系数,所构建的流变应力方程能准确地描述热变形过程中合金的流变应力行为。微观组织观察表明在变形初期合金组织主要为动态回复组织,随着应变增加,逐渐转变为再结晶组织。     

A Model to Predict Recrystallization Kinetics in Hot Strip Rolling Using Combined Artificial Neural Network and Finite Elements

A thermo-mechanical model has been developed to establish a coupled heat conduction and plastic flow analysis in hot-rolling process. This model is capable of predicting temperature, strain, and strain rate distributions during hot rolling as well as the subsequent static recrystallization fraction and grain size changes after hot deformation. Finite element and neural network models are coupled to assess recrystallization kinetics after hot rolling. A new algorithm has been suggested to create differential data sets to train the neural network. The model is then used to predict histories of various deformation variables and recrystallization kinetics in hot rolling of AA5083. Comparison between the theoretical and the experimental data shows the validity of the model.     

THE HOT DEFORMATION BEHAVIOR AND DYNAMIC RECRYSTALLIZATION MODEL OF 35CrMo STEEL

The isothermal single-stage compression of 35CrMo structural steel has been carried out by using Gleeble 1500 simulator at the temperature range of 950℃ to 1150℃ and strain rate range of 0.01s-1 to 10s-1. The effect of hot deformation parameters, such as strain rate, deformed temperature and initial grain size on the flow stress behavior was investigated. The activation energy of tested alloy was calculated, which is 378.16kJ/mol; The relationships between the peak stress (σp), the peak stain (εp), the critical strain (εc) and Z parameter were established. The micro structure evolution shows the pre-existing austenite grain boundaries constitute the principal nucleation sites for dynamic recrystallization (DRX), and the initial austenite grain size affects the grain size of DRX slightly. The kinetic mathematical model of DRX of 35CrMo is: XDRX=1-exp(-3.23-2.28) and Ddyn = 2.252× 10Z-0.22.     

Static Recrystallization of 30Cr2Ni4MoV Ultra-Super-Critical Rotor Steel

In order to investigate the static recrystallization (SRX) behavior of 30Cr2Ni4MoV ultra-super-critical rotor steel, the double-hit hot compression tests were conducted in the deformation temperature range of (970-1250) °C, the strain rate range of (0.001-0.1) s^?1, and the inter-pass time range of (1-100) s. It is found that the effects of forming parameters (forming temperature and strain rate) on the microstructural evolution during SRX are not significant, while those of the initial austenitic grain size are obvious only when the initial austenitic grain size is less than 225.4 µm. Based on the experimental results, the kinetic equations have also been developed to predict the SRX behaviors of hot-deformed 30Cr2Ni4MoV steel. The proposed kinetic equation correlates well with the experimental results confirming that the proposed kinetic equations can give an accurate estimate of the static softening behaviors for 30Cr2Ni4MoV steel.     

核电用304不锈钢静态再结晶模型的建立

利用Gleeble-1 500 D热力模拟试验机,对304不锈钢进行了热压缩模拟试验。研究了变形温度在950℃~1 200℃之间,变形速率为1×10-3 s-1、1×10-2 s-1、1×10-1 s-1,变形量为50%的变形行为及组织特征,建立了304钢的静态再结晶晶粒尺寸模型。结果表明：变形量、变形温度、应变速率因素的影响较大;应变量越大,变形温度越低,应变速率越高,晶粒越细;304钢静态再结晶晶粒尺寸模型的建立为大锻件静态再结晶数值模拟分析提供了可靠的判据。     

21CrMo10钢高温塑性变形性能

研究21CrMo10钢的塑性变形性能,对制造热作模具具有重要的意义。文章利用Gleeble 1500D热力模拟机,在不同的温度和变形速率条件下对21CrMo10钢进行试验,测得了P91不同变形条件下的真实应力-真实应变曲线。试验曲线表明,21CrMo10钢在变形的过程中存在着动态再结晶;而且,随着温度的升高或应变速率的降低,其流变应力下降。对比试验得出的变形曲线认为,FORGE 2005材料库的变形曲线由于未考虑到动态结晶过程,不符合实际。对各种变形条件下的峰值流变应力进行分析得出,流变应力基于Zener-Holloman参数存在函数关系。     

晶粒度对690合金热变形特性的影响

利用物理模拟实验方法对具有不同晶粒尺寸的690合金试样进行热压缩变形实验,变形温度范围为1100～1200℃,应变速率分别为0.1,1,10s-1,获得了合金的流变应力数据,并对合金变形后的组织特征进行了分析,建立了包含初始晶粒度参数的本构关系模型。结果表明:晶粒尺寸增大使690合金高温变形时的流变应力增加,发生动态再结晶的临界应变增大,动态再结晶体积分数减小,根据所建立的流变应力本构模型计算出的流变应力值与实验值相近,从而完善了690合金的热变形本构方程。     

17CrNiMo6钢的静态再结晶行为

采用Gleeble-1500热模拟试验机,在压缩温度为950~1050 ℃(间隔50 ℃)、预应变为0.1~0.2(间隔0.05)、应变速率为0.01~1 s^-1、不同原始晶粒尺寸和道次间隔时间条件下,对17CrNiMo6钢进行双道次热压缩试验。讨论了道次间隔时间、压缩温度、预应变、应变速率和原始晶粒尺寸对17CrNiMo6钢静态再结晶行为的影响。根据回归分析得到静态再结晶在不同变形条件下的流变应力曲线,结合压缩后试样的显微组织,建立了17CrNiMo6钢静态再结晶动力学模型和晶粒尺寸模型。结果表明,17CrNiMo6钢静态再结晶体积分数随压缩温度、间隔时间、预应变和应变速率增加而增大;静态再结晶晶粒尺寸随压缩温度和原始奥氏体晶粒尺寸增加而增大,随预应变和应变速率的增加而减小。通过对比所建模型的预测值与热压缩所得的试验值,发现二者较为吻合,验证了模型的准确性。     

EFFECT OF INITIAL GRAIN SIZE ON STATIC RECRYSTALLIZA-TION SOFTENING IN Cr STEEL USING STRESS RELAXATION TECHNIQUE

Effect of initial grain size (I.G.S.) on static recrystallization softening in Cr steel (0.77wt. % Cr) has been investigated through the use of interrupted hot compression tests and stress relaxation curves from Gleeble 1500. Initial grain sizes were varied between 20 and 93 microns. Stress strains curves for Cr steel for different initial grain sizes and recrystallization times have been highlighted. Similar observation was made for metadynamic recrystallization with shorter retardation times. Statically recrystallized grain size also increased as initial grain size increases. It is found that the values of initial grain size have significant effects on the mean flow stress and static recrystallization kinetics as well as the peak strain values to initiate dynamic recrystallization.     

Zr对Ti-Mo复合微合金化钢形变奥氏体静态再结晶动力学和析出相的影响

通过在Gleeble-3500热模拟试验机上进行双道次压缩模拟试验,研究了Ti-Mo复合微合金化钢和Ti-Zr-Mo复合微合金化钢在875、925、975和1025 ℃四个温度下形变奥氏体的静态再结晶过程。分析了两种试验钢在双道次压缩模拟时的真应力-真应变曲线,建立了两种试验钢的静态再结晶动力学模型,计算了两种试验钢奥氏体静态再结晶激活能,采用高分辨透射电镜观察了不同温度双道次压缩后两种试验钢中形变诱导析出相和大颗粒未溶相的形貌和种类,并对试验钢的形变储能密度进行了简单比较。结果表明,Zr的添加可以提高Ti-Mo复合微合金化钢在变形过程中的变形抗力,使试样在热变形过程中积累的形变储能增多,同时降低形变奥氏体的静态再结晶激活能,使奥氏体的再结晶更容易发生。Zr可以替代Ti与O、S等形成大颗粒未溶相,使试验钢静态再结晶过程中析出更多细小弥散的形变诱导析出相,使试验钢中形变奥氏体的静态再结晶过程出现延迟。     

Simulation of Static Recrystallization After Cold Side-Pressing of Low Carbon Steels Using Cellular Automata

In this article, the finite element and cellular automata models are coupled to determine static recrystallization kinetics after cold deformation of low carbon steels. The deformation analysis is first performed to predict the strain, stress, and stored energy distributions within the deformed steel employing the finite element software, ABAQUS. Then, the kinetics of static recrystallization and distribution of recrystallized grain size are evaluated by means of a cellular automata model together with the stored energy calculated by the deformation analysis. To examine the predictions, the experimental results of recrystallized fractions and grain sizes after cold side-pressing of low carbon steel are compared with the predicted ones, and a reasonable agreement is achieved.     

Hot Deformation and Corrosion Resistance of High-Strength Low-Alloy Steel

The hot deformation characteristics and the corrosion behavior of a high-strength low-alloy(HSLA) steel were investigated at deformation temperatures ranging from 800 to 1100 ℃ and strain rates ranging from 0.1 to 10 s-1 using an MMS-200 thermal simulation testing machine. Based on the flow curves from the experiment, the effects of temperature and strain rate on the dynamic recrystallization behavior were analyzed. The flow stress decreased with increasing deformation temperature and decreasing strain rate. With the assistance of the process parameters, constitutive equations were used to obtain the activation energy and hot working equation. The hot deformation activation energy of HSLA steel in this work was 351.87 kJ/mol. The work hardening rate was used to determine the critical stress(strain) or the peak stress(strain). The dependence of these characteristic values on the Zener-Hollomon parameter was found. A dynamic recrystallization kinetics model of the tested HSLA steel was constructed, and the validity of the model was confirmed by the experimental results. Observation of the microstructures indicated that the grain size increased with increasing deformation temperature,which led to a lowered corrosion resistance of the specimens.     

工业纯钛TA1的双道次热压缩变形及软化行为

在Gleeble-3500热模拟试验机上对工业纯钛TA1进行单、双道次等温热压缩试验,变形温度为650~850 ℃,道次间隙时间为1~60 s,变形速率为10 s^-1,研究了工业纯钛TA1单、双道次热压缩过程中静态软化和动态软化行为。利用光学显微镜对变形后的微观组织进行观察,研究了工业纯钛TA1在不同变形条件下的微观组织演变。结果表明,工业纯钛TA1在单、双道次热压缩变形过程中表现出明显的硬化和软化行为,峰值应力前表现为加工硬化,峰值应力后表现为加工软化,最终达到动态软化和加工硬化的动态平衡。在道次间隙时间内发生静态软化,静态软化程度随着道次间隙时间的增加和温度的升高而增大。随着道次间隙时间的延长和温度的升高,道次间再结晶更加充分,第二道次变形后晶粒尺寸增加更明显,当发生完全再结晶时,软化程度达到最大。在热压缩变形期间,发生动态软化,650 ℃和750 ℃时以动态再结晶为主,850 ℃时以动态回复为主。     

高强合金钢50SiMnVB动态再结晶模型研究

通过热模拟压缩试验研究了50SiMnVB合金钢在应变速率为0.01-10s-1、温度为800-1000 ℃条件下的高温热变形行为.利用金相显微镜观察了合金压缩变形后的显微组织,结果表明:50SiMnVB合金钢在高温热变形过程中发生了典型的动态回复和动态再结晶行为,其中,动态再结晶以连续再结晶的形式进行,且应变速率越小、...     

新型低碳含铌热轧H型钢的热变形行为

利用热压缩试验、显微组织分析等手段,研究了一种新型低碳含铌热轧H型钢在1000~1200 ℃变形温度和0.1~5 s^-1应变速率下的热变形行为。分析了变形参数对试验钢微观组织的影响,建立了耦合应变量因素的改进型本构方程,并采用临界比的临界应变模型对发生动态再结晶的临界应变值进行了预测。结果表明:较低应变速率和变形温度下,试验钢的原始奥氏体组织更均匀且平均晶粒尺寸更小;应变速率的升高不利于动态再结晶的发生。发生动态再结晶的临界应变与峰值应变的关系为ε_c/ε_p=0.47。与耦合应变量因素有关的本构方程和临界应变预测模型能较准确地预测各变形温度下低碳含铌热轧H型钢的流变应力和动态再结晶临界应变值。